Viète's formula

Etymology
Named after (1540–1603), who published it in 1593 in his work Variorum de rebus mathematicis responsorum, liber VIII.

Proper noun
\frac{\sqrt2}2\cdot \frac{\sqrt{2+\sqrt2}}2\cdot \frac{\sqrt{2+\sqrt{2+\sqrt2}}}2\cdots$$
 * 1)  An infinite product of nested radicals representing the constant pi: specifically, $$\frac2\pi=